1. Field of the Invention
The invention is directed to double-clutch device, for arranging in a drivetrain of a motor vehicle between a drive unit and a transmission, wherein the clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission.
2. Description of the Related Art
A clutch device of this type is known, for example, from EP 0 931 951 A1. The clutch device serves to connect the drive of a motor vehicle with a multiple-speed shift transmission via two friction clutches which are preferably automatically actuated, wherein a disengagement or release system is allocated to each of these two friction clutches, so that the two friction clutches can be engaged or released independently from one another. A clutch disk of one of the two friction clutches is arranged on a central transmission input shaft so as to be fixed with respect to rotation relative to it, while a clutch disk of the other friction clutch engages at a second transmission input shaft so as to be fixed with respect to rotation relative to it, this second transmission input shaft, constructed as a hollow shaft, enclosing the central transmission input shaft. The known double-clutch is arranged with a fixed thrust plate of one friction clutch at a flywheel of an internal combustion engine. To this extent, the arrangement of the double-clutch in a drivetrain substantially corresponds to the arrangement of conventional (single-)friction clutches in the drivetrain.
Double-clutch devices (called simply double-clutches) of the type mentioned above have attracted great interest recently and are generally formed of two wet or dry clutches which are switched alternately, possibly also with overlapping. Particularly in connection with a multiple-speed shift transmission, clutches of this type make it possible to carry out shifting processes between two respective transmission speeds of the transmission without interruption of tractive forces.
In principle, double-clutch devices make it possible for both clutches to be applied jointly in especially difficult starting processes, particularly those common in car racing. For this purpose, the accelerator pedal can be deflected to its stop, as the case may be, while the motor vehicle is kept essentially stationary at the same time by applying the maximum braking force until the clutch has reached its optimal transmission point. When the braking action is canceled at the moment of reaching the optimal transmission point, the vehicle is started with maximum acceleration. Starting processes of this kind are also considered for motor vehicles with a relatively weak engine under extreme starting conditions, for example, when starting on an obstruction; that is, they are not considered only for racing cars.
Obviously, starting processes of the type described above lead to high slippage with a correspondingly extensive development of heat. This presents the problem of carrying away this heat from the area of the friction clutch serving as starting clutch. Further, a correspondingly high wear of the friction clutch must be taken into account. Moreover, heating of the friction clutches is accompanied by changes in the coefficient of friction of the friction clutches, so that control of the release mechanisms of the two friction clutches, and therefore control of the two friction clutches relative to one another, can be appreciably impaired. Since inaccuracies or changes in the functional matching of the two friction clutches relative to one another caused by heat can have the result that a torque ratio not intended in the shifting process is applied to the transmission input shafts, shifting processes in the shift transmission can be subjected to load. The synchronization in the shift transmission can be overtaxed in this way, so that, in the worst case, the shift transmission can be damaged to the point of complete failure, apart from disadvantages with respect to efficiency which occur in any case. On the whole, mismatching between the two friction clutches caused by heat is incompatible with a problem-free torque transmission in shifting processes in the shift transmission without interruption of tractive force and without jerking during shifting.
Another problem area in a double-clutch device relates to starting processes carried out in opposition to an inclination, wherein the motor vehicle must be prevented from rolling backward, or those which are used when parking at the lowest possible speed, for example, for precise positioning of a motor vehicle in a parking space. The operating states mentioned above are referred to in technical circles as xe2x80x9chill-holdingxe2x80x9d and xe2x80x9ccreepingxe2x80x9d. Both starting processes have in common that the friction clutch serving as starting clutch is operated, sometimes without actuation of the accelerator, over a longer period of time with slip. Although the torques to be transmitted in such starting processes lie well below those occurring under the operating conditions described above, especially in car racing, an intensive heating of the respective friction clutch or even both friction clutches can occur, resulting in the problems detailed above.
Suggestions have been made for gear-shifting strategies and shifting processes for double-clutch transmissions based on the aimed for adjustment of clutch slip (DE 196 31 983 C1) with consequent generation of friction heat. Depending on driving behavior, overheating problems of the type mentioned above cannot be ruled out.
The risk of intensive overheating exists not only in a dry friction clutch, but can also occur in so-called xe2x80x9cwetxe2x80x9d friction clutches, in the form of a disk or plate clutch, which are operated by the action of a viscous operating medium such as hydraulic fluid. By way of example, a gear change box with two plate clutches is known from DE 198 00 490 A1, wherein one plate clutch is provided for forward driving and the other for driving in reverse. DE 198 00 490 A1 is concerned primarily with providing adequate cooling of the two plate clutches using the viscous operating medium. In spite of the liquid cooling, heating of the friction clutches is also a considerable problem in plate clutches because the operating medium, which usually flows through friction facing grooves or the like to carry off the heat, cannot be guided between the plates in optional quantity. The reason for this is that, on one hand, excessive flow through the friction facing grooves or the like would build up a counterpressure between the friction surfaces of two adjacent plates and would therefore reduce the capacity of the friction clutches to transmit torque (with a corresponding increase in slip and therefore additional generation of friction heat, so that the problem of overheating is exacerbated) and, on the other hand, the operating medium could be overheated and destroyed when flowing through between the plates. Overheating in plate clutches can result in that the friction surfaces can no longer separate from one another completely during a disengaging process and, consequently, torques can still be transmitted via the clutch which should be disengaged, so that considerable drag torques can reach the associated shift transmission. When plates clutches are used in a multiple-clutch device, especially a double-clutch device, of the type mentioned above, shifting processes could again be brought under load in the shift transmission with resulting overtaxing of the synchronization in the shift transmission.
One approach to mastering overheating problems in the area of friction clutches in case of unfavorable operating conditions, for example, with problematic starting processes in a motor vehicle, is to provide another starting element in addition to the first and second clutch arrangements which is in the form of a hydraulic clutch or hydrodynamic clutch and comprises a hydrodynamic circuit with an impeller wheel, a turbine wheel and, if desired, a stator wheel. The driving member can be connected in parallel with one of the two friction clutches; that is, it can act on a common transmission input shaft irrespective of the engagement state of this friction clutch. A clutch device in which two plate clutches and a starting element of this type are integrated, was described in the German Patent Application 199 46 857.5 by the present Applicant which was applied for on Sep. 30, 1999 and whose disclosure is incorporated in the subject matter disclosed in the present application.
Within the framework of investigations undertaken by the present Applicants in connection with double-clutch devices, it was shown in general that wet-type clutches exhibit sealing problems and problems relating to output losses. Further, it was shown that boundary conditions relating to the available axial and radial installation space could be adhered to only with difficulty, if at all, based on the previously known concepts. With regard to clutches, possibly, diaphragm clutches, which are actuated by pistons integrated in the clutch device, the arrangement of the piston chambers associated with the pistons proved especially problematic.
The object of the invention is generally to achieve improvements with respect to at least one of the problems and/or other problems mentioned above. In particular, an objective of the invention is to provide a multiple-clutch device with advantageous operating performance, for example, with respect to operating reliability, and/or a multiple-clutch device which can be constructed in a compact manner.
According to a first aspect, the invention provides a multiple-clutch device, i.e., a double-clutch device, for arranging in a drivetrain of a motor vehicle between a drive unit and a transmission, wherein the clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission. According to this first aspect of the invention, at least one of the clutch arrangements has an actuating piston defining a pressure chamber for actuation, preferably for engagement of the clutch arrangement by means of a pressure medium, preferably a hydraulic medium, wherein the actuating piston divides the pressure chamber from an associated centrifugal force pressure compensation chamber holding a pressure compensation medium which compensates for increases in pressure in the pressure chamber caused by centrifugal force and, consequently, for forces on the actuating piston caused by centrifugal force.
The centrifugal force pressure compensation chamber can be connected to a pressure compensation medium supply in order to supply pressure compensation medium to the centrifugal force pressure compensation chamber at least in a requested operating state of the clutch device. The pressure compensation medium supply can be formed by a hydraulic medium supply or a separate operating fluid supply, possibly an operating oil supply, which also serves to supply at least one other functional unit of the clutch unit.
When a return spring or restoring spring arrangement is provided for restoring the actuating piston, this restoring spring arrangement can be received in the centrifugal force pressure compensation chamber in order to economize on installation space.
It is particularly preferable that a sealing arrangement associated with the pressure compensation chamber and/or a boundary wall of the pressure compensation chamber are/is so arranged and so constructed in an elastic manner that they/it at least reinforce/reinforces a disengagement of the clutch arrangement in a stroke area of the actuating piston comprising a stroke position of the actuating piston corresponding to an engaged state of the respective clutch arrangement. The sealing arrangement and/or boundary wall can accordingly assume the function of a spring element which reinforces or brings about the opening of the actuating piston. As a rule, the above-mentioned restoring spring arrangement is additionally provided to move the piston to its rest position corresponding to a fully released clutch arrangement. The reinforcement of the releasing movement provided by the sealing arrangement and/or boundary wall is particularly advisable insofar as it often comes about that the clutch arrangement can be released quickly, for example, when the clutch arrangement is to be operated with regulated slip. Various factors can work against a quick release, for example, inertial forces which are exerted on the piston by a cooling fluid, especially cooling oil, or inertial forces which are mediated by the cooling fluid and act on the piston or which are based on the mass moment of inertia; as a rule, these inertial forces are particularly prominent when the piston releasing movement is introduced. For this reason, it is useful to reinforce the introduction of the piston releasing movement in the suggested manner above all.
The sealing arrangement can have a sealing element which is arranged at a wall portion defining the pressure compensation chamber and can engage tightly with the latter and with the actuating piston. The sealing element can project from the wall portion in the direction of the stop face of the actuating piston and, at least in the engaged state of the clutch arrangement, can transmit elastic restoring forces to the actuating piston in the direction of a stroke position corresponding to a released state of the clutch arrangement. The sealing element can be injection-molded at an edge area of the wall portion or can be fitted over the edge area. This is particularly simple in terms of assembly and, moreover, provides for a secure positioning of the sealing element at the wall portion.
According to a second independent aspect of the invention, for a double-clutch device, for arranging in a drivetrain of a motor vehicle between a drive unit and a transmission, wherein the clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission, it is suggested that at least one of the clutch arrangements has an actuating piston defining a pressure chamber for actuation, preferably for engagement of the clutch arrangement by means of a pressure medium, preferably a hydraulic medium, and that the clutch arrangements are constructed as plate clutch arrangements, of which a radial outer clutch arrangement annularly encloses a radial inner clutch arrangement, wherein the actuating piston associated with the radial outer clutch arrangement is guided at a plate carrier, preferably an outer plate carrier, of the radial outer clutch arrangement and at a plate carrier, preferably an outer plate carrier, of the radial inner clutch arrangement so as to be axially displaceable and so as to seal the pressure chamber.
As a result of the above-mentioned guiding of the actuating piston at the plate carriers, the actuating piston is axially guided in a secure manner so that high operating reliability is achieved and, on the other hand, an especially compact construction of the clutch device is made possible, since no separate guide elements are required for guiding the piston and installation space can accordingly be economized on. When a centrifugal force pressure compensation chamber is provided, which receives the pressure compensation medium and is defined or limited by the actuating piston, the actuating piston can also guide the centrifugal force pressure compensation chamber at the plate carrier in a sealing manner.
With respect to an especially compact construction of the clutch device, it is further suggested that the centrifugal force pressure compensation chamber associated with the radial outer clutch arrangement is defined by a plate carrier, preferably an outer plate carrier, of the radial inner clutch arrangement. Accordingly, a separate wall for forming the pressure compensation chamber can be completely dispensed with, if desired.
Installation space can also be economized on in a corresponding manner in that an actuating piston associated with the radial inner clutch arrangement is guided so as to be axially displaceable at a plate carrier, preferably an outer plate carrier, of the radial inner clutch arrangement and, as the case may be, at a wall of a centrifugal force pressure compensation chamber, if provided, which is associated with the actuating piston, and so as to seal the associated pressure chamber and, as the case may be, the centrifugal force pressure compensation chamber which receives the pressure compensation medium. In this connection, it is advisable that sealing elements cooperating with the actuating pistons are arranged so as to be radially staggered and preferably partially overlapping axially.
With respect to an optimum utilization of the installation space, it can be provided that at least one of the centrifugal force pressure compensation chambers extends over a different radial area than the associated pressure chamber in such a way that an effective pressure application surface of the piston on the pressure chamber side is smaller than an effective pressure application surface of the piston on the pressure compensation chamber side and/or that a pressure compensation chamber limiting surface of the piston extends farther radially outward than a pressure chamber limiting surface of the piston. In order to avoid an overcompensation of the centrifugal force which could possibly occur when the pressure compensation chamber is completely filled with pressure compensation medium (in this regard, the radius dependency of the pressure increase in the pressure chamber and in the pressure compensation chamber caused by centrifugal force must be taken into account), fill level limiting means can be allocated to the pressure compensation chamber to limit the filling of the pressure compensation chamber with pressure compensation medium to a maximum radial partial filling level. The fill level limiting means can comprise at least one pressure compensation medium through-opening in a wall of the pressure compensation chamber extending in radial direction.
According to a third independent aspect of the invention, for a double-clutch device, for arranging in a drivetrain of a motor vehicle between a drive unit and a transmission, which clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission, it is suggested that at least one of the clutch arrangements has an actuating piston defining a pressure chamber for actuation, preferably for engagement of the clutch arrangement by means of a pressure medium, preferably a hydraulic medium, wherein the actuating piston is guided at a wall portion defining the pressure chamber and/or at a wall portion defining an associated pressure compensation chamber and/or so as to seal the pressure compensation chamber, wherein a labyrinth seal comprising at least one annular groove in a surface portion of the actuating piston and/or of the wall portion, which surface portion extends in an engaging-disengaging direction of the actuating piston, acts between the respective wall portion and the piston, and/or wherein at least one sealing ring acts between the respective wall portion and the piston, which sealing ring is secured to one actuating piston and wall portion on the one hand and acts at the other actuating piston and wall portion with axial play relative to one actuating piston and wall portion on the other hand and is acted upon during an engaging movement and/or during a disengaging movement of the actuating piston such that the sealing engagement with the wall portion and/or actuating piston increases.
When a labyrinth seal of the type mentioned above is provided, separate sealing elements made of rubber, plastic or elastomer material, for example, can be dispensed with and the seal and associated counter-element can be made of the same material with, consequently, the same thermal coefficient of expansion. It is extremely advantageous for both sealing members of the labyrinth seal to have the same thermal coefficient of expansion insofar as temperature changes or temperature fluctuations cause no changes, or no substantial changes, in the engagement or frictional engagement, as the case may be, between the sealing members which would lead to corresponding fluctuations in inertial forces to be overcome during the engaging and disengaging movement of the piston. Further, there are no substantial fluctuations in the sealing action, especially no loss of tightness.
The other constructional variant according to the invention with the sealing ring which is fixed on one side and engages with axial play on the other side is advantageous insofar as particularly good sealing can be achieved, for example, when the sealing ring is additionally acted upon by the pressure in the pressure chamber or pressure compensation chamber to strengthen the sealing engagement in such a way that the sealing ring is pressed more firmly into a shaped portion receiving the sealing ring. This takes place to a marked degree in the case of the pressure chamber when the clutch is engaged with the stationary piston in its moved out or disengaged position, i.e., when the plate stack is tensioned to a maximum degree and as little leakage as possible should occur.
It is assumed in the preceding remarks that the sealing ring is acted upon to increase the sealing engagement during an engaging movement and reaches a maximum sealing engagement in the end position of the actuating piston. However, if it should seem advisable, the maximum sealing engagement could also be provided in a middle stroke position of the piston or in the end position of the actuating piston corresponding to a released clutch.
The sealing ring can engage in an annular groove of the actuating piston or of the wall portion. Further, the sealing ring can have at least one portion which acts, for example, in the manner of a stripper, at a surface region of the actuating piston or of the wall portion which extends in an engaging-disengaging direction of the actuating piston and which is plane in this direction.
It is suggested that the sealing ring is curved in axial direction in a state of lower tension with a looser sealing engagement with respect to a section plane containing or parallel to an axis of rotation of the clutch device and is moved to a state of higher tension with a tighter sealing engagement during an engaging movement and/or during a disengaging movement of the actuating piston in that it is stretched with respect to the section plane or is less sharply curved in axial direction.
As was already indicated, it is preferred in general that the sealing ring is acted upon to the maximum sealing engagement in the engaged state of the respective clutch arrangement.
The wall portion defining the pressure chamber can be a plate carrier, preferably an outer plate carrier, of the respective clutch arrangement constructed as plate clutch arrangement.
When the sealing ring is inserted into a shaped portion or cutout of the actuating piston on one side and acts at the plane surface portion on the other side, axial installation space can be economized on in that the shaped portion is provided in the edge area of a radially extending piston portion. Thin wall thicknesses are made possible in this way. The shaped portion, possibly, a groove, can then be rolled in if desired. In order to economize on axial installation space, it is also helpful that the sealing ring can be elongated in cross section in radial direction as suggested according to the invention without the risk of impairing the sealing action.
According to a fourth aspect of the invention, for a double-clutch device, for arranging in a drivetrain of a motor vehicle between a drive unit and a transmission, which clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission, it is suggested that each of the clutch arrangements has an actuating piston defining a pressure chamber for actuation, preferably for engagement of the clutch arrangement by means of a pressure medium, preferably a hydraulic medium, wherein a radial outer sealing element (designated as first sealing element with respect to the pressure chamber) which seals the pressure chamber of the first clutch arrangement on the radial outer side and/or axially and which acts between the actuating piston and a wall of the pressure chamber and a radial outer sealing element (designated as second sealing element with respect to the pressure chamber) which seals the pressure chamber of the second clutch arrangement on the radial outer side and/or axially and which acts between the actuating piston and a wall of the pressure chamber are arranged at different radial distances from an axis of rotation of the clutch device, and/or wherein a radial inner sealing element (designated as third sealing element with respect to the pressure chamber) which seals the pressure chamber of the first clutch arrangement at the radial inner side and/or axially and which acts between the actuating piston and a wall of the pressure chamber and a radial inner sealing element (designated as fourth sealing element with respect to the pressure chamber) which seals the pressure chamber of the second clutch arrangement at the radial inner side and/or axially and which acts between the actuating piston and a wall of the pressure chamber are arranged at different radial distances from an axis of rotation of the clutch device.
Due to the different radial spacing of the sealing elements provided according to the invention, the radial and/or axial installation space of the clutch device can be kept comparatively small. In order to make possible a particularly compact construction of the clutch device, it is suggested in a further development that the first and second sealing elements and/or the third and fourth sealing elements are so arranged with respect to a section plane containing or parallel to the axis of rotation of the clutch device that a straight line which intersects both sealing elements encloses, with an axis of rotation of the clutch device, an angle xcex1 of approximately 10xc2x0 to 70xc2x0, preferably approximately 20xc2x0 to 50xc2x0, most preferably approximately 30xc2x0 to 40xc2x0, at least in the disengaged state of the two clutch arrangements and/or in the engaged state of the two clutch arrangements.
The actuating piston preferably divides the respective pressure chamber from an associated pressure compensation chamber which receives a pressure compensation medium. For this purpose, it is suggested by way of a further development that a radial outer sealing element (designated as fifth sealing element with respect to the pressure compensation chamber) which seals the pressure compensation chamber of the first clutch arrangement on the radial outer side and/or axially and which acts between the actuating piston and a wall of the pressure compensation chamber and a radial outer sealing element (designated as sixth sealing element with respect to the pressure compensation chamber) which seals the pressure compensation chamber of the second clutch arrangement on the radial outer side and/or axially and which acts between the actuating piston and a wall of the pressure compensation chamber are arranged at different radial distances from an axis of rotation of the clutch device, and/or that a radial inner sealing element (designated as seventh sealing element with respect to the pressure compensation chamber) which seals the pressure compensation chamber of the first clutch arrangement on the radial inner side and/or axially and which acts between the actuating piston and a wall of the pressure compensation chamber and a radial inner sealing element (designated as eighth sealing element with respect to the pressure compensation chamber) which seals the pressure compensation chamber of the second clutch arrangement on the radial inner side and/or axially and which acts between the actuating piston and a wall of the pressure compensation chamber are arranged at different radial distances from an axis of rotation of the clutch device.
According to this suggestion, a construction of the clutch device which is comparatively compact radially and/or axially can be achieved in spite of the provided pressure compensation chambers especially when the fifth and sixth sealing elements and/or the seventh and eighth sealing elements are so arranged with respect to a section plane containing or parallel to the axis of rotation of the clutch device that a straight line which intersects both sealing elements encloses, with an axis of rotation of the clutch device, an angle xcex1 of approximately 10xc2x0 to 70xc2x0, preferably approximately 30xc2x0 to 60xc2x0, most preferably approximately 40xc2x0 to 50xc2x0, at least in the disengaged state of the two clutch arrangements and/or in the engaged state of the two clutch arrangements.
It is suggested for the sealing elements mentioned above that the first and the fifth sealing element are separate sealing elements which are preferably arranged at an essentially identical radial distance from the axis of rotation of the clutch device, and/or that the second and the sixth sealing elements are separate sealing elements which are preferably arranged at an essentially identical radial distance from the axis of rotation of the clutch device, and/or that the third and the seventh sealing elements are formed by a sealing element associated with both the pressure chamber and the pressure compensation chamber, and/or that the fourth and the eighth sealing elements are formed by a sealing element associated with both the pressure chamber and the pressure compensation chamber. In general, however, the seals can also be arranged on different diameters, wherein a matching of the pressures in the piston chambers can be achieved by selecting the diameters so as to be adapted to one another.
The features of a multiple-clutch device and a drivetrain which were indicated in connection with the different aspects of the invention can be advantageously combined. Further independent aspects of the invention will be discerned by the person skilled in the art from the preceding explanations and the description of the Figures.
The invention is further directed to a drivetrain for a motor vehicle with a clutch device, according to at least one aspect of the invention, arranged between a drive unit and a transmission.
The invention will be described more fully in the following with reference to embodiment examples shown in the Figures.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.